Wave motion in a narrow gap coupling with the roll motion of a vessel next to an offshore terminal

Abstract

Concerning the scenario of a vessel operating alongside an offshore terminal, the vessel being the floating body and the offshore terminal bottom-mounted. The closeness of the two bodies leads to the formation of a long narrow gap, within which the large amplification of the water-surface elevation could occur. The coupling effect between the roll motion of the vessel and the water-surface motion within the gap is primarily concerned. Under the assumption that the quay wall of the terminal is infinitely long and fully reflective, the imaging principle and a modified Green's function have been developed to investigate such an effect. Numerical models are developed based on the two proposed approaches, respectively, in conjunction with a higher-order boundary element method. For a small gap width, the p = 1 resonant mode of water-surface motion in the gap can apparently enhance the roll motion of the vessel. The radiation wave owing to the enhanced roll motion can in turn disturb the water-surface motion, increasing the frequency of the dominant peak while decreasing its amplitude. As the gap width increases, the water-surface elevation around the resonant frequency of roll motion gets more and more noticeable, gradually becoming the dominant peak. The effect of the mooring stiffness is also discussed, revealing the existence of a ꞌnon-resonance regionꞌ where no resonance occurs in this specific frequency region. It is also noted that the resonant water-surface motion of p = 1 mode can cause a remarkable amplification of the negative horizontal mean wave drift force, pushing the vessel away from the terminal.